SAT-558 - Massive Prostatic Solitary Fibrous Tumor Causing IGF-2 Mediated Non-Islet Cell Tumor Hypoglycemia: A Case of Doege-Potter Syndrome.

Background: Doege-Potter syndrome is a rare paraneoplastic cause of non-islet cell tumor hypoglycemia (NICTH) due to ectopic insulin-like growth factor 2 (IGF-2) secretion, mostly associated with solitary fibrous tumors (SFTs). Most SFTs arise in the thoracic cavity, while pelvic and prostatic involvement is rare, and IGF-2-mediated hypoglycemia secondary to prostate SFT has not previously been described.

Case: An 82-year-old man with diet-controlled type 2 diabetes mellitus and a large prostatic mass was admitted for a stage IV sacral ulcer. During the hospitalization, he developed asymptomatic recurrent fasting hypoglycemia (serum glucose of nadir 19–26 mg/dL, requiring repeated intravenous dextrose.
He was hemodynamically stable with preserved oral intake and no hypoglycemia-inducing medications. His morning serum cortisol was 8.4 µg/dL and ACTH 13.1 pg/mL, with an appropriate rise of cortisol to 20.5 µg/dL at 60 minutes after 250-µg cosyntropin.
During a supervised fast, biochemical evaluation at a plasma glucose of 30 mg/dL demonstrated appropriate suppression of insulin ( < 0.4 µIU/mL; RR 2.6–24.9, C-peptide (0.4 ng/mL; RR 1.1–4.4), and proinsulin (1.7 pmol/L; RR 0–10), with normal beta-hydroxybutyrate (0.05 mmol/L; RR 0.02–0.27), undetectable insulin antibodies, and a negative sulfonylurea screen.. Computed tomography of the abdomen/pelvis confirmed a 16 cm prostate mass invading the bladder. Further studies showed low IGF-1 (29 ng/mL; RR 40–194), upper normal IGF-2 (542 ng/mL; RR 267–616), with an IGF-2/IGF-1 ratio of 18 (>10 diagnostic for NICTH). Prostate biopsy confirmed an SFT positive for CD34 and vimentin. Hypoglycemia resolved with glucocorticoid therapy (dexamethasone 3 mg daily); however, poor functional status precluded surgical or systemic treatment.

Discussion: NICTH results from overproduction of high-molecular-weight IGF-2 due to dysregulated expression of IGF-2 and subtilisin/kexin type 4, the enzyme responsible for pro-IGF-2 processing, leading to accumulation of incompletely processed IGF-2 that activates insulin receptors and causes hypoglycemia. Prior review of prostatic SFTs describes primarily local obstructive or mass-effect symptoms without reported metabolic complications. Accordingly, this case represents a novel endocrine presentation that expands the anatomic spectrum of SFT-associated NICTH. While surgical resection is curative, in those who are not candidates, glucocorticoid therapy can improve hypoglycemia, as in our case. This case underscores the importance of considering paraneoplastic hypoglycemia in patients with unexplained fasting hypoglycemia and large mesenchymal tumors, even when arising in rare locations such as the prostate.

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